1. Field of the Invention
The invention relates to a membrane bag. The bag comprises two separation membranes interconnected at their rims and having supply and drain conduits. The invention also relates to a winding module made of the membrane bag as well as a method of producing the membrane bag and winding module. 2. Description of the Related Prior Art
In the prior art, separation membranes consist of a thin, comparatively permeable carrier foil. On one side of the carrier foil an active coating is applied. This is the so-called asymmetrical separation membrane. There also exist separation membranes consisting exclusively of the active layer itself. Also, so-called symmetrical separation membranes are known. These membranes have an active coating on both sides of a carrier foil.
A great number of polymers, such as cellulose derivatives, e.g., cellulose acetate, various polyamides, polysulfones and also inorganic materials, such as graphite oxide and zirconium hydroxide, are known as active coatings. The active coatings usually have a thickness of between 10.sup.-3 to 10.sup.-1 mm.
Membrane bags and winding modules are used in apparatuses for carrying out membrane separation methods, such as inverted osmosis, ultra or microfiltration, gas separation and pervaporations. In these methods, the media to be treated, i.e. liquids, solutions or vapors, are guided past a separation membrane under pressure. As a result of the pressure, certain components of the media which are permeable to the membrane pass through the membrane as permeate.
In the prior art membrane bags and winding modules, the separation membranes have simply been glued together at their rims and subsequently sewn, stapled or clamped together at the glued rim regions. However, the media in the interior of the membrane bags and winding modules is under substantial pressure of up to approximately 80 bars. Only in separation membranes consisting sometimes sufficiently durable to withstand the pressure. At higher temperatures, or a multi-layer separation membrane system, the prior art membrane bags are not satisfactory. The connections leak, or with multi-layer membranes, the inner active coating becomes detached.